37.3.2. Freelite and Hevylite Precision on the SPAPLUS
The SPAPLUS maintains precision through a combination of acid/alkali cuvette washing and an innovative reaction cuvette mixing system. Air pressure is used in place of stirrers to mix the reaction mixture in a U-shaped cuvette. No physical contact is made with the reaction mixture, thereby removing any possibility of carry-over on a stirrer. Assessment of the performance of SPAPLUS CSF assays by Benard et al. and Laurent et al. indicated that carry over was not observed during routine use, and that serum and CSF analysis can be effectively integrated on a single SPAPLUS instrument to optimise laboratory workflow.
During Freelite assay validation, assay precision was assessed using 3 control fluids that ranged in concentration from 7.2 mg/L to 142.1 mg/L. The maximum intra- and inter-assay imprecision for κ or λ Freelite assays was 3.4% and 4.2%, respectively. An independent study by Ludwig et al. reported within run precision of 2.5-7% and 2.2-2.3% for Freelite κ and λ sFLC assays, respectively. The authors also assessed the day-to-day performance and identified precision of 3.3-3.6% and 5.3-6.1% for Freelite κ and λ, respectively. These findings have been replicated by a number of other laboratories.
A precision study of the 6 Hevylite reagents, by Mirbahai et al. reported maximum intra- and inter-assay imprecision of 3.2% and 4.7%, respectively. Jacobs et al. assessed the routine performance of Hevylite assays using routine clinical samples and a number of EQA samples. All 6 Hevylite assays demonstrated excellent precision, with CV results that varied between 2.2-7.4%. These findings were supported by Arkir et al. who described intra- and inter-assay precision of 0.7-2.9% and 1.5-8.3%, respectively.